Heretofore, various methods have been proposed as methods for producing dichloropentafluoropropanes (HCFC-225) represented by chemical formula: C3HCl2F5. For example, a method for obtaining dichloropentafluoropropanes by contacting dichlorofluoromethane with tetrafluoroethylene in the presence of a modified aluminum chloride catalyst has been proposed, and technology for applying isomerization to various isomeric mixtures of dichloropentafluoropropanes obtained by this method, has been disclosed (see e.g. Patent Document 1, Non-Patent Document 1).
Among the dichloropentafluoropropanes (HCFC-225), attention by the present applicant is paid to HCFC-225ca which can be a starting material for synthesizing 2,3,3,3-tetrafluoropropene (CF3CF═CH2; HFO-1234yf). That is, in recent years, it is considered to use HFO-1234yf or the like having a small ozone depletion potential, as a refrigerant, and usefulness of HCFC-225ca is being increased as a starting material to obtain 1,1-dichloro-2,3,3,3-tetrafluoropropene (CF3CF═CCl2; CFO-1214ya) as raw material for HFO-1234yf.
Under such circumstances, a method for efficiently obtaining HCFC-225ca has been found wherein, in order to efficiently obtain HCFC-225ca, a predetermined raw material is subjected to an isomerization reaction by partially fluorinated alumina (see Patent Document 2).
Further, in order to obtain a desired compound not limited to the above compound, various methods for isomerization by transposing substituents are known by using, as raw material, an organic compound containing chlorine atoms or fluorine atoms. As a catalyst for the isomerization reaction in such a case, a fluorinated alumina obtained by partially fluorinating an alumina, is known to be useful (see e.g. Patent Documents 3 and 4).